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Hummel, Michelle

Publications and source records attributed to Hummel, Michelle.

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

2D Polyhedral Template Matching for Atomic Resolution Microscopy

SAND2024-13879O The 2D Polyhedral Template Matching for Atomic Resolution Microscopy is a suite of functions for analyzing atomic resolution electron microscopy images using the 2D polyhedral template matching (2D-PTM) method. This software analyzes atomic resolution microscopy data from electron microscopic imaging or scanning probe microscopies. The primary application is for identifying different crystal phases, crystal orientations, and defect structures obtained in such atomic resolution images. Written in MATLAB and starting from an atomic resolution image, the code identifies the positions of atomic intensity peaks. It then matches predefined structural templates to the local atomic environments. Outputs include the local structural identification, the template scaling factor and rotation angle, root-mean-squared deviation (RMSD), and centrosymmetry parameter.

Medlin, Douglas↗
DOE OSTI2016

Restoring the Grand Canyon Ecosystem: Evidence from Dynamic Systems Theory

Constructing and operating dams for hydropower generation can impact downstream ecosystems by altering natural flow regimes and interfering with the lifecycles of aquatic and riparian species. Increased concern from environmental interests, coupled with federal relicensing requirements that aim to minimize environmental impacts, have put pressure on dam operators to quantify the flow regime changes that have resulted from dam construction and to evaluate how future modifications to dam releases may impact river systems. In this study, we present a method for analyzing the impact of dam operations by reconstructing system trajectories from hydrologic flow time series for different periods of dam operation (pre-dam, post-dam, and post-modification). We apply these methods to flow data from Lees Ferry, Colorado, just downstream of Glen Canyon Dam on the Colorado River, to determine how the dimensionality of the river system has changed over time and to evaluate the effectiveness of a new operating policy put into place after the 1992 Grand Canyon Protection Act was passed. While the post-dam period governed by hydropower operations is characterized by high dimensional, stochastic behavior, the pre-dam and post-modification periods are low dimensional and less complex, demonstrating the success of the new operating policy in mirroring the natural flow regime. Our analysis also suggests that applying a strictly deterministic or stochastic modeling approach to historical flow data does not appropriately capture the varying complexity of the Colorado River system during the three distinct periods of hydrologic behavior.

13 HYDRO ENERGY↗
DOE OSTI2016

Restoring Flow Regimes after Dam Construction and Operation: Evidence from Dynamic Systems Theory

Dams provide a variety of benefits to society, including hydropower generation, flood control, recreation, and water supply for municipal, industrial, and agricultural customers. However, constructing and operating dams for these purposes can negatively impact downstream ecosystems by altering natural flow regimes and interfering with the lifecycles of aquatic and riparian species. Increased concern from environmental interests has put pressure on dam operators to quantify the flow regime changes that have resulted from dam construction and to evaluate how future modifications to dam releases may impact river systems. In this study, we present a method for analyzing the impact of dam operations by reconstructing system trajectories from hydrologic flow time series for different periods of dam operation (pre-dam, post-dam, and post-modification). We apply these methods to flow data from eight rivers in the US to determine the dimensionality of each operating period and to analyze trends based on the primary purpose of dam operation. Hydropower dams operated without flow restrictions exhibit high dimensional, stochastic behavior. However, the system dimensionality is reduced to approximately three variables when ramping restrictions are implemented, or in cases where an afterbay is present to reregulate flows. This low dimensional behavior is more similar to natural flow regimes. For dams operated primarily for flood control or water supply, the flow regimes are typically low dimensional and more deterministic.

13 HYDRO ENERGY↗